Solid component of catalyst for the (co)polymerization of ethylene

ABSTRACT

A solid component of a catalyst for the (co)polymerization of ethylene is composed of a silica carrier and a catalytically active part which includes titanium, magnesium, chlorine and also alkoxy groups, and is obtained: by suspending an activated silica in an ethanolic solution of magnesium chloride; by contact of the suspension with an alkoxy or halogen alkoxyde of titanium and with a silicon halide; by eliminating the ethanol from the resulting suspension in order to recover a solid matter; and by making this solid react with an aluminum alkyl chloride.

DESCRIPTION

The present invention concerns a solid component of catalyst, theprocedure for its preparation and its use in the polymerization ofethylene and the copolymerization of ethylene with alfa-olefins.

It is known that ethylene, or generally alfa-olefins, can be polymerizedat low pressure with Ziegler-Natta type catalysts. These catalysts areusually composed of a compound of elements from subgroups IV to VI ofthe periodic table (compounds of transition metals), mixed with anorganometallic compound, or hydride, of the elements in groups I to IIIof the periodic table.

Catalysts are also known in the art, in which the compound of transitionmetal is fixed to a solid carrier, either organic or inorganic, andsometimes physically and/or chemically treated. Examples of such solidcarriers are the oxygenated compounds of bivalent metals (such asoxides, inorganic oxygenated salts and carboxylates) or hydroxychloridesor the chlorides of bivalent metals. According to U.S. Pat. No.3.642.746, a carrier for catalysts is a bivalent metal halide treatedwith an electron donor. According to the description of U.S. Pat. No.4.421.674, a carrier for catalysts is a solid, smooth product obtainedby the spray drying of a solution of magnesium chloride in ethanol. Inparticular, U.S. Pat. No. 4.421.674 specifies that microspheroidalparticles of a solid such as silica can be suspended in the ethanolsolution of magnesium chloride, to obtain a spherical carrier forcatalysts, having a nucleus composed of the microspheroidal solid andlined with a layer of activated magnesium chloride.

It has now been discovered that it is possible to obtain solid compoundsof Ziegler-Natta catalysts on a carrier prepared with microspheroidalsilica and a solution of magnesium chloride in ethanol, using a simpleand covenient procedure which not only overcomes the difficulties andcomplications involved in spray drying, but also produces solidcomponents of catalysts having a surprisingly improved catalyticactivity in the (co)polymerization of ethylene.

In accordance with this, the present invention concerns a procedure forthe preparation of a solid component of catalyst for the polymerizationof ethylene and the copolymerization of ethylene with alfa-olefins,composed of a carrier of silica in particles (50-90% by weight) and acatalytically active part (50-10% by weight) including titanium,magnesium, chlorine and also alkoxy groups. This procedure ischaracterized by the following stages:

(a) a solution of magnesium chloride in ethanol is prepared;

(b) an activated silica in particles is impregnated using the solutionprepared under (a), by suspending the silica particles in the solution;

(c) at least one titanium compound chosen from alkoxides and halogenalkoxides of titanium and a silicon halide, is added to the suspension(b), with an atomic ratio between the magnesium, in the magnesiumchloride, and the titanium ranging from 2.0/1 to 12.1/1 and a ratiobetween the silicon atoms and alkoxy groups, in the alkoxide or halogenalkoxide of titanium, ranging from 0.1/1 to 4.0/1;

(d) the ethanol is eliminated from the suspension obtained in (c), byevaporation, to recover a solid;

(e) the solid obtained in (d) is reacted with an alkyl aluminiumchloride, with an atomic ratio between the chlorine atoms, in the alkylaluminium chloride, and the alkoxy groups, in the alkoxide or halogenalkoxide of titanium, ranging from 0.5/1 to 7.0/1; and

(f) the solid component of the catalyst is recovered.

A solution of magnesium chloride in ethanol is prepared in phase (a) ofthe procedure. For this purpose, it is preferable to use totally oralmost totally anhydrous magnesium chloride, almost totally referring toa water content which is lower than approx. 5% by weight. Similarly, theethanol is preferably anhydrous or can have a low water content which ishowever less than approx. 5% by weight. The dissolving of the magnesiumchloride can take place at room temperature (20°-25° C.), or at highertemperatures to reach the reflux point of the ethanol at atmosphericpressure. The preferred operating temperature is approx. 60° C., withthe preparation of ethanol solutions having a concentration of magnesiumchloride from 1 to 15% by weight.

In phase (b) of the procedure described in the present invention, silicain particles is impregnated using the solution prepared in (a), bysuspending the silica particles in the solution.

The most suitable silica for this purpose is a microspheroidal, poroussilica having a particle size ranging from 10 to 100 μm, a SiO₂ contentof >90% by weight, a surface area ranging from 250 to 400 m² /g, volumeof the pores ranging from 1.3 to 1.8 ml/g and average diameter of thepores ranging from 20 to 30 nm. This silica should undergo activationtreatment before being impregnated, which can be carried out either byheating the silica in an inert atmosphere, at a temperature ranging fromapprox. 100° C. to approx. 650° C., over a period from 1 to 20 hours, orby putting the silica in contact with a organometallic compound, such asa magnesium alkyl or an aluminium alkyl, such as magnesium butyl, octylmagnesium butyl and aluminium triethyl, operating at room temperature orat higher temperatures , for example approx. 60° C. It is preferable forthe silica to be activated by treatment with octyl magnesium butyl, inquantities of approx. 10-20% by weight of silica.

Impregnation is carried out by suspending from 10 to 20 parts by weightof silica for every 100 parts by volume of the ethanol solution ofmagnesium chloride, and contact is maintained, if necessary under slightstirring, at a temperature which is brought from room temperature(20°-25° C.) to the approximate boiling point of the ethanol, preferablyto approx. 50°-65° C., over a period from 0.5 to 2.0 hours.

According to the present invention, in phase (c) of the procedure, atleast one titanium compound chosen from alkoxides and halogen alkoxidesof titanium and a silicon halide, is added to the suspension (b), withan atomic ratio between the magnesium, in the magnesium chloride, andthe titanium, ranging from 2.0/1 to 12.0/1, and a ratio between thesilicon atoms and alkoxy groups, in the alkoxide or halogen alkoxide oftitanium, ranging from 0.1/1 to 4.0/1.

The titanium compounds most suited for this purpose are alkoxides andchloroalkoxides of titanium, containing from 1 to 4 carbon atoms in thealkoxide portion. Specific examples of these compounds are: titaniumtetra-n-propylate, titanium tetra-n-butylate, titaniumtetra-i-propylate, titanium tetra-i-butylate and the correspondingtitanium mono- or di-chloroalkoxies. These alkoxies can be mixed withtitanium tetrachloride, however, it is preferable to use a mixture oftitanium tetrachloride and a titanium tetraalkoxide, chosen from thoselisted above, with a molar ratio between them of approx. 1/3.

In accordance with the present invention, a silicon halide is added tothe suspension of phase (b), chosen from silicon tetrahalides andhalogen silanes. Specific examples of these compounds are: silicontetrachloride, trichlorosilane, vinyl trichlorosilane, trichloroethoxysilane, chloroethyl trichlorosilane. For this purpose, silicontetrachloride is preferred.

In phase (c) of the procedure, it is preferable to operate with anatomic ratio between the magnesium and titanium from 3.5/1 to 8.5/1 andwith a ratio between the silicon atoms and alkoxy groups ranging from0.5/1 to 4.0/1.

According to a particular application of the present invention, acompound of zirconium or hafnium, chosen from halides, particularlytetrachlorides alkoxides and halogen alkoxides, particularlychloroalkoxides, should be added to suspension (b), in such quantitiesas to have an atomic ratio between the titanium and zirconium or hafniumfrom 0.5/1 to 2.0/1. In this way, a solid component of catalyst isobtained, which is useful in the polymerization of ethylene obtainingpolymers with a wide distribution of molecular weight.

In phase (c) of the procedure, there is no specific order for theaddition of the compounds of titanium, silicon and, if any, zirconium orhafnium. However this addition is carried out, the resulting suspensionis kept at a temperature ranging from room temperature (20°-25° C.) toapprox. 100° C., over a period of from 0.5 to 3 hours, preferably at atemperature of around 60° C., for approx. 1 hour.

In phase (d) of the procedure, the ethanol is eliminated from thesuspension obtained in (c) by means of evaporation. This evaporationshould be carried out by distilling the ethanol at atmospheric pressureor at a reduced pressure and finally drying the solid for 0.5 to 2 hoursat a temperature of approx. 120° C., under a pressure of 5-10 mm Hg.

In phase (e) of the procedure, the solid obtained in (d) is reacted withan alkyl aluminium chloride, with an atomic ratio between the chorineatoms, in the alkyl aluminium chloride, and the alkoxy groups, of thealkoxide or halogen alkoxide of titanium, ranging from 0.5/1 to 7.0/1.

More specifically, in phase (e) the solid is suspended in an inerthydrocarbon liquid such as hexane or heptane, and is put in contact withan aluminium chloride alkyl, generally chosen from diethyl aluminiumchloride, ethyl aluminium sesquichloride, diisobutyl aluminium chlorideand isobutyl aluminium dichloride, dissolved in the above hydrocarbonsolvent or in a different hydrocarbon solvent. The process is carriedout at a temperature ranging from 10° to 100° C, for a period which,depending on the chosen operating temperature, can vary from 10 minutesto 24 hours, to obtain an atomic ratio between the chlorine and titaniumin the solid ranging from 10/1 to 40/1. The preferred operatingtemperature is from 20° to 90° C, for a period of from 10 minutes to 1hour, to obtain an atomic ratio between the chlorine and titanium in thesolid of from 12/1 to 36/1. This treatment has the effect of increasingthe chlorine content in the solid component of catalyst, with acontemporary reduction, either partial or total, of the titanium fromthe tetravalent state to the trivalent state, and with the partial ortotal elimination of the alkoxy groups present.

At the end of the treatment, the solid component of catalyst isrecovered in phase (f), is washed with a liquid aliphatic hydrocarbonsolvent, such as hexane or heptane, until the chlorides have beeneliminated from the washing liquid, and finally dried.

The solid component of catalyst, according to the present invention, iscomposed of a silica carrier in particles (50-90% by weight) and acatalytically active part (50-10% by weight) including titanium,magnesium and chorine, and also alkoxy groups, with the following atomicratios: Mg/Ti from 2.0/1 to 12.0/1; Cl/Ti from 10/1 to 40/1, alkoxygroups/Ti from 0/1 to 20/1. These alkoxy groups include ethoxy groupsoriginating from the ethanol and alkoxy groups deriving from thetitanium alkoxide used. The quantity of titanium in the component ofcatalyst generally varies from 0.5 to 5.0% by weight. The solidcomponent of catalyst is preferable composed of a silica carrier inparticles (55-80% by weight) and a catalytically active part 45-20% byweight) containing titanium, magnesium, chlorine and alkoxy groups, withthe following atomic ratios: Mg/Ti from 3.5/1 to 8.5/1; Cl/Ti from 12/1to 36/1, alkoxy groups/Ti from 2/1 to 10/1. In this component ofcatalysts the quantity of titanium generally varies from 0.8 to 2.0% byweight.

When zirconium or hafnium is present in the solid component ofcatalysts, the atomic ratio between the titanium and zirconium orhafnium will range from 0.5/1 to 2.0/1.

The present invention also concerns a catalyst for the(co)polymerization of ethylene, composed of the above-mentioned solidcomponent of catalysts, combined with an organometallic compound ofaluminium (co-catalyst) chosen from aluminium trialkyls and aluminiumalkyl halides (particularly chlorides), containing from 1 to 5 carbonatoms in the alkyl section. Among these, aluminium trialkyls arepreferred with from 2 to 4 carbon atoms in the alkyl section, such asaluminium triethyl, aluminium tributyl and aluminium triisobutyl. Thecatalyst of the present invention has an atomic ratio between thealuminium (in the co-catalyst) and titanium (in the solid component ofcatalysts) which generally ranges from 20:1 to 250:1, preferably from100:1 to 200:1.

This catalyst is extremely active in procedures for the polymerizationof ethylene and the copolymerization of ethylene with alfa-olefins. Theuse of silicon halide, under the conditions described above, isessential for obtaining this activity, as can be seen from theexperimental examples which follow. In particular, it has been provedthat silicon halide makes solid components of catalysts highly activeeven when there is a high content of alkoxy groups and also in the caseof solid components of catalysts containing zirconium or hafnium inaddition to titanium.

The catalyst of the present invention can be used in polymerizationprocesses carried out by means of the suspension technique in an inertdiluent or using the method of the gas phase, in a fluidized or stirredbed. The alfa-olefins which can be copolymerized are generally thosecontaining from 3 to 10 carbon atoms, preferably from 4 to 6 carbonatoms, such as butene-1, hexene-1 and 4-methyl-pentene-1. The generalpolymerization conditions are: temperature from 50° to 100° C, totalpressure from 5 to 40 bar, with a ratio between the partial pressures ofhydrogen and ethylene of from 0 to 10. There is, at any rate, highproductivity in the olefinic polymer and the polymer thus obtained hasan excellent rheological properties and, in particular, is in the formof granules which are non-friable and without fines.

In the experimental examples which follow and which are intended toprovide a better illustration of the present invention, amicrospheroidal silica carrier is used, having a particle size rangingfrom 20 to 60 μm, a SiO₂ content of >99% by weight, surface area of 320m² /g, pore volume of 1.65 ml/g and average pore diameter of 25-26 nm.

EXAMPLE 1 (comparison)

4.5 g (47.3 mmoles) of anhydrous magnesium chloride and 100 ml ofabsolute ethanol anhydrified on aluminium are charged into a 250 mlflask equipped with a reflux coolant, mechanical stirrer andthermometer. The mixture is heated to 60° C. for 30 minutes to allow forthe complete dissolution of the magnesium chloride.

15 g of microspheroidal silica, previously activated by contact for 30minutes at 60° C. with a solution containing 17 ml of 20% by weight ofoctyl magnesium butyl in heptane and 150 ml of n-hexane, are suspendedin the solution thus obtained. The suspension is kept at a temperatureof 60° C. for 30 minutes.

2.4 g (7.05 mmoles) of titanium tetrabutylate and 0.445 g (2.35 mmoles)of titanium tetrachloride are added to the suspension and contact ismaintained at 60° C. for 1 hour.

It is then dried by evaporating the solvent and the solid recovered isheated under vacuum (5-10 mm Hg) at a temperature of 120° C. for 1 hour.

12 g of the solid thus obtained are suspended in 40 ml of anhydrousn-hexane and 9.6 ml of a 40% by weight solution of aluminium ethylsesquichloride (3.23 g; 13.03 mmoles) in n-decane, are added to theresulting suspension. Contact is maintained for 15 minutes at atemperature of 25° C. The solid is then recovered by filtration, washedwith anhydrous n-hexane until all the chlorides in the washing liquidhave been eliminated, and finally dried by evaporating the solvent.

Approx. 10 g of a solid component of catalyst are thus obtained, insolid granule form, containing 58% by weight of silica and having aratio Mg:Ti:Cl:alkoxy groups of 7.2:1.0:16.6:9.4.

The solid component of catalyst prepared in the above way, is used in atest for the polymerization of ethylene. More specifically, thepolymerization is carried out in a 5 liter autoclave containing 2 litersof n-hexane. The process is carried out at a pressure of 15 bar, in thepresence of hydrogen, with a ratio between the pressure of the hydrogenand that of the ethylene of 0.47/1, at a temperature of 90° C. and overa period of 2 hours, using 100 mg of the solid component of catalyst andaluminium triethyl as a co-catalyst, with an atomic ratio between thealuminium in the co-catalyst, and the titanium in the solid component ofcatalysts, of 190/1.

A yield equal to 2.4 kg of polyethylene per gram of the solid componentof catalyst is thus obtained and the polyethylene has the followingcharacteristics:

    ______________________________________                                        density:                0.9595  g/ml                                          (ASTM D-1505)                                                                 MFI (2.16 kg):          1.38    g/10'                                         (Melt-Flow Index -ASTM D-1238)                                                apparent density:       0.315   g/ml                                          (ASTM D-1895)                                                                 MFR:                    30.0                                                  ______________________________________                                         (MFR = MeltFlow Index Ratio, defined as a ratio MFI (21.6 kg)/MFI (2.16       kg)).                                                                    

The polyethylene is in granule form with the following size distributionin um:

    ______________________________________                                               >2000    0.1                                                                  2000< >1000                                                                            6.9                                                                  1000< >500                                                                             77.0                                                                 500< >250                                                                              14.0                                                                 <250     2.0                                                           ______________________________________                                    

EXAMPLE 2 Comparison

4.5 g (47.3 mmoles) of anhydrous magnesium chloride and 100 ml ofabsolute ethanl anhydrified on aluminium, are charged in a nitrogenatmosphere into a 250 ml flask equipped with a reflux coolant,mechanical stirrer and thermometer. The mixture is heated to 60° C. for30 minutes to allow for the complete dissolution of the magnesiumchloride.

15 g of microspheroidal silica, previously activated by contact for 30minutes at 60° C. with a solution containing 17 ml of 20% by weightbutyl octyl magnesium in heptane and 150 ml of n-hexane, are suspendedin the solution thus obtained. The suspensione is kept at a temperatureof 60° C. for 30 minutes.

2.4 g (7.05 mmoles) of titanium tetrabutylate and 0.445 g (2.35 mmoles)of titanium tetrachloride are then added to the suspension and contactis maintained at 60° C. for 1 hour.

It is then dried by evaporating the solvent and a solid is recovered,which is heated under vacuum (5-10 mm Hg) to a temperature of 120° C.for 1 hour.

12 g of the solid thus obtained are suspended in 40 ml of anhydrousn-hexane and 19.2 ml of a 40% by weight solution of aluminium ethylsesquichloride in n-decane (6.45 g; 26.06 mmoles) are added to theresulting suspension. Contact is maintained for 1 hour at a temperatureof 65° C. The solid is then recovered by filtration, washed withanhydrous n-hexane until all the chlorides in the washing liquid havebeen eliminated, and finally dried by evaporation of the solvent.

Approx. 10 g of a solid component of catalysts are thus obtained, insolid granule form, containing 56% by weight of silica and having aratio Mg:Ti:Cl:alkoxy groups of 6.3:1.0:18.9:6.0.

The solid component of catalyst prepared in the above way, is used in atest for the polymerization of ethylene. More specifically, thepolymerization is carried out in a 5 liter autoclave containing 2 litersof n-hexane. The process is carried out at a pressure of 15 bar, in thepresence of hydrogen, with a ratio between the pressure of the hydrogenand that of the ethylene of 0.47/1, at a temperature of 90° C. over aperiod of 2 hours, using 100 mg of the solid component of catalysts andaluminium triethyl as a co-catalyst, with an atomic ratio between thealuminium, in the co-catalyst, and the titanium, in the solid componentof catalyst, of 180/1.

A yield equal to 4.2 kg of polyethylene per gram of the solid componentof catalyst, is obtained and the polyethylene has the followingcharacteristics:

    ______________________________________                                        density:             0.9606  g/ml                                             MFI (2.16 kg):       2.16    g/10'                                            apparent density:    0.30    g/ml                                             MFR:                 31                                                       ______________________________________                                    

The polyethylene is in granule form with the following size distributionin um:

    ______________________________________                                               >2000    8.4                                                                  2000< >1000                                                                            19.9                                                                 1000< >500                                                                             63.7                                                                 500< >250                                                                              6.9                                                                  <250     1.1                                                           ______________________________________                                    

EXAMPLE 3

4.5 g (47.3 mmoles) of anhydrous magnesium chloride and 100 ml ofabsolute ethanol anhydrified on aluminium are charged in a nitrogenatmosphere into a 250 ml flask equipped with a reflux coolant,mechanical stirrer and thermometer. The mixture is heated to 60° C. for30 minutes to allow for the complete dissolution of the magnesiumchloride.

15 g of microspheroidal silica, previously activated by contact for 30minutes, at 60° C., with a solution containing 17 ml of 20% by weightbutyl octyl magnesium in heptane and 150 ml of n-hexane, are suspendedin the solution thus obtained. The suspension is kept at a temperatureof 60° C. for 30 minutes.

2.4 g (7.05 mmoles) of titanium tetrabutylate, 0.445 g (2.35 mmoles) oftitanium tetrachloride, 3.3 ml (4.84 g, 28.52 mmoles) of silicontetrachloride, are then added to the suspension and contact ismaintained at 60° C. for 1 hour.

It is then dried by evaporating the solvent and a solid is recovered,which is heated under vacuum (5-10 mm Hg) to a temperature of 120° C.for 1 hour.

13.5 g of the solid thus obtained are suspended in 50 ml of anhydrousn-hexane and 12.7 ml of a 40% by weight solution of aluminium ethylsesquichloride in n-decane (4.03 g; 16.29 mmoles), are added to theresulting suspension. Contact is maintained for 15 minutes at atemperature of 25° C. The solid is then recovered by filtration, washedwith anhydrous n-hexane until all the chlorides in the washing liquidhave been eliminated, and finally dried by evaporation of the solvent.

12 g of a solid component of catalyst are thus obtained, in solidgranule form, containing 62% by weight of silica and having a ratioMg:Ti:Cl:alkoxy groups of 7.2:1.0:18.9:5.4.

The solid component of catalyst prepared in the above way, is used in atest for the polymerization of ethylene. More specifically, thepolymerization is carried out in a 5 liter autoclave containing 2 litersof n-hexane. The process is carried out at a pressure of 15 bar , in thepresence of hydrogen, with a ratio between the pressure of the hydrogenand that of the ethylene of 0.47/1, at a temperature of 90° C., over aperiod of 2 hours, using 50 mg of the solid component of catalyst andaluminium triethyl as a co-catalyst, with an atomic ratio between thealuminium, in the co-catalyst, and the titanium, in the solid componentof catalysts, equal to 200/1.

A yield equal to 10.4 kg of polyethylene per gram of the solid componentof catalyst, is obtained and the polyethylene has the followingcharacteristics:

    ______________________________________                                        density:             0.9589  g/ml                                             MFI (2.16 kg):       2.2     g/10'                                            apparent density:    0.28    g/ml                                             MFR:                 29.9                                                     ______________________________________                                    

The polyethylene is in granule form with the following size distributionin um:

    ______________________________________                                               >2000    4.1                                                                  2000< >1000                                                                            31.2                                                                 1000< >500                                                                             52.2                                                                 500< >250                                                                              8.1                                                                  <250     4.4                                                           ______________________________________                                    

EXAMPLE 4 Comparison

4.5 g (47.3 mmoles) of anhydrous magnesium chloride and 100 ml ofabsolute ethanol anhydrified on aluminium are charged in a nitrogenatmosphere into a 250 ml flask equipped with a reflux coolant,mechanical stirrer and thermometer. The mixture is heated to 60° C. for30 minutes to allow for the complete dissolution of the magnesiumchloride.

15 g of microspheroidal silica, previously activated by contact for 30minutes, at 60° C., with a solution containing 17 ml of 20% by weightbutyl octyl magnesium in heptane and 150 ml of n-hexane, are suspendedin the solution thus obtained. The suspension is kept at a temperatureof 60° C. for 30 minutes.

3.20 g (9.40 mmoles) of titanium tetrabutylate, 3.60 g (9.38 mmoles) ofzirconium tetrabutylate, are then added to the suspension and contact ismaintained at 60° C. for 1 hour.

It is then dried by evaporating the solvent and a solid is recovered,which is heated under vacuum (5-10 mm Hg) to a temperature of 120° C.for 1 hour.

11 g of the solid thus obtained are suspended in 100 ml of anhydrousn-hexane and 30 ml of a 40.5% by weight solution of aluminium isobuthyldichloride in n-hexane (9.72 g; 62.7 mmoles), are added to the resultingsuspension. Contact is maintained for hour at a temperature of 65° C.The solid is then recovered by filtration, washed with anhydrousn-hexane until all the chlorides in the washing liquid have beeneliminated, and finally dried by evaporation of the solvent.

10 g of a solid component of catalyst are thus obtained, in solidgranule form, containing 53.5% by weight of silica and having a ratioMg:Ti:Zr:Cl:alkoxy groups of 6.5:1.0:1.0:24.8:4.1.

The solid component of catalyst prepared in the above way, is used in atest for the polymerization of ethylene. More specifically, thepolymerization is carried out in a 5 liter autoclave containing 2 litersof n-hexane. The process is carried out at a pressure of 15 bar , in thepresence of hydrogen, with a ratio between the pressure of the hydrogenand that of the ethylene of 0.47/1, at a temperature of 90° C., over aperiod of 2 hours, using 150 mg of the solid component of catalyst andaluminium triethyl as a co-catalyst, with an atomic ratio between thealuminium, in the co-catalyst, and the titanium, in the solid componentof catalyst, equal to 140/1.

A yield equal to 4.1 kg of polyethylene per gram of the solid componentof catalyst, is obtained and the polyethylene has the followingcharacteristics:

    ______________________________________                                        density:             0.9636  g/ml                                             MFI (2.16 kg):       2.9     g/10'                                            apparent density:    0.30    g/ml                                             MFR:                 37.8                                                     ______________________________________                                    

The polyethylene is in granule form with the following size distributionin um:

    ______________________________________                                               >2000    0.1                                                                  2000< >1000                                                                            26.7                                                                 1000< >500                                                                             64.7                                                                 500< >250                                                                              7.4                                                                  <250     1.1                                                           ______________________________________                                    

EXAMPLE 5

4.5 g (47.3 mmoles) of anhydrous magnesium chloride and 100 ml ofabsolute ethanol anhydrified on aluminium are charged in a nitrogenatmosphere into a 250 ml flask equipped with a reflux coolant,mechanical stirrer and thermometer. The mixture is heated to 60° C. for30 minutes to allow for the complete dissolution of the magnesiumchloride.

15 g of microspheroidal silica, previously activated by contact for 30minutes, at 60° C., with a solution containing 17 ml of 20% by weightbutyl octyl magnesium in heptane and 150 ml of n-hexane, are suspendedin the solution thus obtained. The suspension is kept at a temperatureof 60° C. for 30 minutes.

3.20 g (9.40 mmoles) of titanium tetrabutylate 3.60 g (9.38 mmoles) ofzirconium tetrabutylate, and 8.0 ml (11.74 g, 69.13 ml) of silicontetrachloride, are then added to the suspension and contact ismaintained at 60° C. for 1 hour.

It is then dried by evaporating the solvent and a solid is recovered,which is heated under vacuum (5-10 mm Hg) to a temperature of 120° C.for 1 hour.

18.6 g of the solid thus obtained are suspended in 100 ml of anhydrousn-hexane and 37 ml of a 40.5% by weight solution of aluminium isobuthyldichloride in n-hexane (11.9 g; 77.34 mmoles), are added to theresulting suspension. Contact is maintained for 1 hour at a temperatureof 65° C. The solid is then recovered by filtration, washed withanhydrous n-hexane until all the chlorides in the washing liquid havebeen eliminated, and finally dried by evaporation of the solvent.

Approx. 17 g of a solid component of catalyst are thus obtained, insolid granule form, containing 50% by weight of silica and having aratio Mg:Ti:Zr:Cl:alkoxy groups of 8.2:1.0:1.0:36.2:17.1.

The solid component of catalyst prepared in the above way, is used in atest for the polymerization of ethylene. More specifically, thepolymerization is carried out in a 5 liter autoclave containing 2 litersof n-hexane. The process is carried out at a pressure of 15 bar , in thepresence of hydrogen, with a ratio between the pressure of the hydrogenand that of the ethylene of 0.47/1 at a temperature of 90° C., over aperiod of 2 hours, using 50 mg of the solid component of catalyst andaluminium triethyl as a co-catalyst, with an atomic ratio between thealuminium, in the co-catalyst, and the titanium, in the solid componentof catalyst, equal to 200/1.

A yield equal to 11 kg of polyethylene per gram of the solid componentof catalyst, is obtained and the polyethylene has the followingcharacteristics:

    ______________________________________                                        density:             0.9591  g/ml                                             MFI (2.16 kg):       1.22    g/10'                                            apparent density:    0.23    g/ml                                             MFR:                 35.1                                                     ______________________________________                                    

The polyethylene is in granule form with the following size distributionin um:

    ______________________________________                                               >2000    6.6                                                                  2000< >1000                                                                            40.0                                                                 1000< >500                                                                             42.7                                                                 500< >250                                                                              8.4                                                                  <250     2.3                                                           ______________________________________                                    

What is claimed is:
 1. A proccess for the preparation of a solidcomponent of a catalyst for the polymerization of ethylene and thecopolymerization of ethylene with alfa-olefins, composed of 50-90% bywt. of a carrier of silica particles and 50-10% by wt. of acatalytically active part comprising titanium, magnesium, chlorine andalkoxy groups, comprising the following steps:(a) a solution ofmagnesium chloride in ethanol is prepared; (b) activated silicaparticles are impregnated with the solution prepared under (a) bysuspending the silica particles in the solution; (c) at least onetitanium compound chosen from alkoxides and halogen alkoxides oftitanium and a silicon halide are added to the suspension prepared in(b), with an atomic ratio between the magnesium, in the magnesiumchloride, and the titanium ranging from 2.0/1 to 12.1/1 and the ratiobetween the silicon atoms and alkoxy groups in the alkoxide or halogenalkoxide of titanium ranging from 01./1 to 4.0/1; (d) the ethanol iseliminated from the suspension obtained in (c) by evaporation to recovera solid; (e) the solid obtained in (d) is reacted with an alkyl aluminumchloride, with an atomic ratio between the chlorine atoms in the alkylaluminum chloride and the alkoxy groups in the alkoxide or halogenalkoxide of titanium, ranging from 0.5/1 to 7.0/1; and (f) the solidcomponent of the catalyst is recovered.
 2. A process according to claim1, characterized by the fact that an ethanol solution with aconcentration of magnesium chloride ranging from 1 to 15% by weight, isprepared in step (a).
 3. A process according to claim 1, characterizedby the fact that in step (b) a microspheroidal silica is impregnated,having a particle size ranging from 10 to 100 μm, a SiO₂ content of >90%by weight, a surface area ranging from 250 to 400 m² g, volume of thepores ranging from 1.3 to 1.8 ml/g and average diameter of the poresranging from 20 to 30 μm, this silica being activated by heating in aninert atmosphere, at a temperature ranging from approximately 100° C. toapproximately 650° C., over a period from 1 to 20 hours, or by puttingthe silica in contact with an organometallic compound selected from thegroup consisting of magnesium alkyl and an aluminum alkyl, operating atroom temperature or at higher temperatures.
 4. A process according toclaim 3, characterized by the fact that in step (b) from 10 to 20 partsby weight of silica for every 100 parts by volume of the ethanolsolution of magnesium chloride are suspended and contact is maintainedat a temperature which is brought from 20°-25° C. to approximately50°-65° C., over a period of from 0.5 to 2.0 hours.
 5. A processaccording to claim 1, characterized by the fact that the titaniumcompounds used in step (c) are selected from the group consisting ofalkoxides and chloroalkoxides of titanium containing from 1 to 4 carbonatoms in the alkoxide portion thereof.
 6. A process according to claim5, characterized by the fact that a mixture of titanium tetrachlorideand a titanium tetraalkoxide, is used, with a molar ratio between themof approx. 1/3.
 7. A process according to claim 1, characterized by thefact that the silicon halide in stage (c) is selected from the groupconsisting of silicon tetrahalides and halogen silanes.
 8. A processaccording to claim 1, characterized by the fact that step (c) of theprocedure is carried out with an atomic ratio between the magnesium andtitanium of from 3.5/1 to 8.5/1 and with a ratio between the siliconatoms and alkoxy groups ranging from 0.5/1 to 2.0/1.
 9. A processaccording to claim 1, characterized by the fact that a compound ofzirconium or hafnium selected from the group consisting of zirconium andhafnium halides, alkoxides and halogen alkoxides is added in step (c),in such quantities as to provide an atomic ratio between the titaniumand zirconium or hafnium of from 0.5/1 to 2.0/1.
 10. A process accordingto claim 1, characterized by the fact that the operating temperature instep (c) ranges from room temperature to about 100° C., over a periodranging from 0.5 to 3 hours.
 11. A process according to claim 1,characterized by the fact that in step (d) of the procedure, the ethanolis eliminated by means of evaporation carried out at either atmosphericpressure or at a reduced pressure and the solid is dried for 0.5 to 2hours at a temperature of about 120° C., under a pressure of 5-10 mm Hg.12. A process according to claim 1, characterized by the fact that instage (e) of the procedure, the solid is reacted with an alkyl aluminiumchloride, with an atomic ratio between the chlorine atoms in the alkylaluminium chloride and the alkoxy groups of the alkoxide or halogenalkoxide of titanium, ranging from 0.5/1 to 7.0/1, operating in an inerthydrocarbon liquid, at a temperature ranging from 10° to 100° C., over aperiod ranging from 10 minutes to 24 hours.
 13. A process according toclaim 12, characterized by the fact that the aluminum chloride alkyl isselected from the group consisting of diethyl aluminum chloride, ethylaluminum sesquichloride, diisobutyl aluminum chloride and isobutylaluminum dichloride, operating at a temperature ranging from 20° to 90°C., for a period of from 10 minutes to 1 hour.
 14. Solid component ofcatalyst obtained according to the process described in claim 1 with 50to 90% by weight of silica and from 50-10% by weight of a catalyticallyactive part including titanium, magnesium and chorine, and also alkoxygroups, with the following atomic ratios: Mg/Ti from 2.0/1 to 12.0/1;Cl/Ti from 10/1 to 40/1, alkoxy groups/Ti from 0/1 to 20/1, and with atitanium content ranging from 0.5 to 5.0% by weight, with respect to theweight of the solid component.
 15. Solid component of catalyst,according to claim 14, with from 55 to 80% by weight of silica and from45 to 20% of a catalytically active part, including titanium, magnesium,chlorine and alkoxy groups, with the following atomic ratios: Mg/Ti from3.5/1 to 8.5/1; Cl/Ti from 12/1 to 36/1, alkoxy groups/Ti from 2/1 to10/1 and with a titanium content ranging from 0.8 to 2.0% by weight,with respect to the weight of the above solid component.
 16. Solidcomponent of catalyst according to claim 14 or 15, with the addition ofeither zirconium or hafnium, with an atomic ratio between the titaniumand zirconium or hafnium ranging from 0.5/1 to 2.0/1.
 17. Catalyst forthe polymerization of ethylene or for the polymerization of ethylenewith alfa-olefins, composed of the solid component of catalyst accordingto claims 14 or 15 and of an organometallic compound of aluminium chosenfrom aluminium trialkyls and aluminium alkyl chlorides, containing from1 to 5, carbon atoms in the alkyl section, with an atomic ratio betweenthe aluminium, in the organometallic compound of aluminium and titanium,in the solid component of catalyst, ranging from 20:1 to 250:1.
 18. Aprocess according to claim 3, wherein the silica is activated by puttingthe silica in contact with an organometallic compound selected from thegroup consisting of magnesium butyl, butyl octyl magnesium and aluminumtriethyl, operating at about 60° C.
 19. A process according to claim 5,wherein the alkoxides and chloroalkoxides of titanium are selected fromthe group consisting of titanium tetra-n-propylate, titaniumtetra-n-butylate, titanium tetra-i-propylate, titanium tetra-i-butylateand the corresponding titanium mono- or di-chloroalkoxides.
 20. Aprocess according to claim 7, wherein the silicon halide is selectedfrom the group consisting of silicon tetrachloride, trichlorosilane,vinyl trichlorosilane, and chloroethyl trichlorosilane.
 21. A processaccording to claim 9, wherein the compound of zirconium or hafnium isselected from the group consisting of zirconium and hafniumtetrachlorides and chloralkoxides.
 22. A process according to claim 10,wherein step (c) is carried out at about 60° C. for a period of about 1hour.
 23. A catalyst according to claim 17, wherein said organometaliccompound of aluminum chosen from aluminum trialkyls and aluminum alkylchlorides contains 2-4 carbon atoms in the alkyl section, with an atomicratio between the aluminum, in the organometallic compound of aluminumand titanium, in the solid component of catalyst, ranging from100:1-200:1.